Mucus transport is a fundamental component of the innate defense of the lung. In many environmental and genetic airways diseases, abnormal mucus transport produces mucus adhesion and, hence, retention. Mucus adhesion drives the pathogenesis of bronchitis by generating airflow obstruction, inflammation, and infection. Perhaps the best documented examples of mucus adhesion-driven bronchitis include patients with acute viral infections, prolonged intubation, and/or CNS disease. In a related context, acute exacerbations (AEs) associated with COPD, CF, and PCD often reflect a component of bronchitic spread to previously normal areas of the lung. Thus, in pulmonary medicine, there is a general need for agents that clear adherent mucus from airways surfaces to provide both symptomatic relief and slow/stop disease progression. Accordingly, our goal is to develop a novel mucolytic to be used as a single agent, or in combination of hydrating agents, to treat mucus retention in patients in need thereof. Based on a novel two-gel hypothesis to better describe the mucociliary apparatus, biophysical formulations have been developed to describe mucus flow in health and failure of flow in disease. These formulations have been extended to analyze the properties of mucus that becomes adherent in disease states and identify strategies to restore transport. We have developed cough machines and other biophysical assays to measure the biophysical forces that generate adhesion and search for pharmacologic agents to restore clearance. This search led to a focus on disulfide bond reducing agents as key additive/synergistic agents with hydrating agents. Inhaled N-acetylcysteine (NAC) has failed in pulmonary medicine because of the poor intrinsic activity of the compound and short half-life on airway surfaces. Consequently, a chemistry program was initiated to identify superior thiol-based scaffolds (e.g., including DTT scaffolds) and apply strategies from related chemistry programs to increase the activity of thiol-based reducing agents and to increase their residence time on airway surfaces. These approaches led to the selection of a lead compound (P2062) that exhibits greatly increased activity over other thiol-based mucolytics (~1,000X), is more durable (longer t1/2) on airway surfaces, and limits cellular penetration and hence has safety advantages over NAC. Our novel reducing agents are active in reducing both MUC5AC and MUC5B in COPD sputum, clearing adherent mucus from the ?ENaC mouse model, clearing adherent mucus from the rhino/sinus cavity from primary ciliary dyskinesia mice, and restoring mucus clearance in neutrophil elastase treated sheep by the tracheal mucus velocity assay. Strategies to optimize P2062 and generate a clinical candidate are outlined in a four tier approach in Specific Aim 1, which focuses on both increases in safety and efficacy. Processes required to move the clinical lead to an IND are outlined in Specific Aim 2, including all of the IND requiring medicinal chemistry, toxicology, ADME, and PK studies. We anticipate immediate initiation of Phase I trials at the end of the CADET funding period.